1 Field of the Invention
This invention generally relates to a molding method and a molding apparatus for fabricating a semiconductor chip package, and more particularly to a molding method and a molding apparatus for a flexible substrate based semiconductor chip package.
2. Description of the Related Art
As electronic devices have become more smaller and thinner, the velocity and the complexity of IC chip become more and more higher. Accordingly, a need has arisen for higher package efficiency. To meet the need, the flexible substrate based ball grid array (BGA) technology has been developed by the semiconductor industry.
FIG. 1 illustrates a molding apparatus for a conventional flexible substrate based BGA package. The molding apparatus comprises a plurality of pots 2. Two substrates 20 are placed at two sides of the pots 2 for supporting a plurality of sets of chips 12 wherein each set of chips 12 are in an array arrangement. Each chip 12 is electrically connected to the substrate 10 through a plurality of bonding wires (not shown). The runner 3 independently extends from one side of the pot 2 to the corner of the substrate 10, and connects to the upper part of a mold disposed on the substrate 10 through a gate 4. Under the pressure created by the plunger 15, the molding compound is forced out of the pot 2 and then passes through the runner 3 and the gate 4 to enter the cavity 11 of the upper part of the mold. When the molding compound fills the cavity 11, the plunger 15 stands still for a predetermined time until the molding compound cures. Then the plunger 15 is raised, the upper part of the mold is opened, and the molded product is removed from the mold. After subsequent processing steps including post-curing, marking, ball mounting and sawing, the singulated substrate based BGA packages are obtained.
FIG. 2a shows a molded product removed from the upper part of the mold. Each set of semiconductor chips 12 on the substrate 10 constitutes an array unit. Each array unit is encapsulated in a unit package body 5. As shown in FIG. 2a, four unit package bodies 5 are individually formed on the substrate 10 and are separated from each other without any connection. Referring to FIG. 2b, the molded product is typically transferred from one processing station to another through sucking at the top surfaces of some of the unit package bodies 5 by suckers 7 during the subsequent processing steps discussed above. However, since the flexible substrate 10 is rather thin (typically smaller than 0.21 mm), the strength of the flexible substrate 10 is too weak to sustain the weight of the unit package bodies 5. When suckers 7 suck at the top surfaces of some of the unit package bodies 5, the weight of the unit package bodies 5 without being sucked will make the flexible substrate 10 bend down. Further, as shown in FIG. 2c, since the mechanical strength of the flexible substrate 10 is not sufficient, a portion of the substrate 10 tends to warp when the substrate 10 with all the molded products thereon is moved along a work surface 1. This adversely affects subsequent processing steps such as post-curing, marking, ball mounting and sawing, even results in peeling between the unit package bodies 5 and the flexible substrate 10, thereby causing damage to the chip 12, traces on the flexible substrate 10, or bonding wires therebetween. As a result, yield losses increase resulting in an increase in manufacturing costs.